The present invention relates generally to multi-component application systems and, more particularly, to an air-stabilized and contained plural component application system and method.
Multi-component application systems have been used, for example, in manufacturing plastic articles by applying resinous materials to a mold or preform for an article, or to pre-arranged fiber reinforcing materials, or to fiber reinforcing materials as they are being applied.
In spraying systems, a liquid resin and a catalyst for the resin are formed into spray particles directed to a substrate where the catalyst and resin react and harden to form the article. In such applications, the resin and catalyst components are preferably mixed together; and the mixture is sprayed onto the substrate. For example, in manufacturing articles with polyester resin, a catalyzing agent for the polyester resin is mixed with the resin; and the resin-catalyst mixture is applied to the substrate. In internal mix systems, the resin and catalyst are mixed within the spraying apparatus; and the mixture is atomized by a spray nozzle and directed onto the substrate. In external mix systems, the resin and catalyst are mixed externally of the apparatus after the resin and catalyst have been atomized. In both external mix and internal mix systems, complete and thorough mixing of the resin and catalyst is important to avoid non-uniform hardening of the resin on the substrate and other undesirable results. Multi-component materials have also been used, for example, in the manufacture of insulating foams by mixing and spraying the components of a foam-producing combination onto a substrate where they produce a hardened foam-like coating. Multi-component application systems have also been developed to divide a pre-mixed flow of plural component material into many small streams for application to fiber reinforcing materials and, in some cases, for application to molds and preforms to provide a coatings layer. Multi-component application systems have thus a multiplicity of applications, each with its specific requirements.
In many spraying systems, large quantities of pressurized air are used to atomize the liquid components. Such systems are expensive to operate and have a number of operational inadequacies. It is expensive to compress air, and the large quantities of compressed air used by existing systems impose a significant operating cost on the system. In addition, the blast of compressed air used to atomize the liquid components carries a significant quantity of spray particles away from the substrate, wastes the expensive material, creates an unclean spray area and generally requires overspray collection systems and contributes to the problem of operating such manufacturing operations safely. Furthermore, the use of large quantities of air during operation of the system can often create an undesirable spread of fumes.
In order to overcome some of the inadequacies attending the use of pressurized air to atomize components dispensed from a spraying apparatus, spraying systems have been developed which incorporate airless atomization techniques.
In prior airless atomization devices, an airless spray nozzle has been used to atomize liquid materials which are pumped at high pressure, that is, pressures generally exceeding 500-600 psi and more frequently in excess of 800 psi, typical operating pressure being 1000-1500 psi. The most commonly used airless nozzle includes an internal, hemispherical passage termination which is cut through by an external, V-shaped groove to form an elongated, elliptical-like orifice. Liquid material pumped at high pressures through such a spray nozzle is forced by the hemispherical termination of the passageway to converge in its flow at and through the elongated orifice. Because of the converging flow at the orifice, the liquid material is expelled through the orifice into a planar, expanding, fan-like film which breaks into spray particles which are carried by their momentum to the article target.
With viscous fluids, high pressures of 1000-1500 psi are required. Such high operating pressures impose a strain on system components reducing their reliability, require generally expensive components in the fluid delivery systems and contribute to the problem of operating such systems safely. Even at high pressures, however, such fan-like films, because they are formed by the convergence of the fluid, include heavy streams at the edges of the planar, fan-like film, which are referred to as "tails". Because of the heavy streamlike flow in the tails, the spray pattern formed by these edge portions of the expanding, fan-like film includes a disproportionate quantity of material and produces a non-uniform deposit with stripes when the spray pattern is swept across a substrate by a spray gun operator. The non-uniform deposit and resulting stripes make the blending of deposited material into a film of uniform thickness virtually impossible.
Past efforts to solve the problem of the tails attending the use of airless spray nozzles have included the insertion of a "preorifice" immediately behind the elongated, elliptical-shaped orifice to concentrate a greater portion of the flow in the central portion of the fan. Although preorifices are helpful, they are not completely satisfactory, adding another source of clogging to the spray gun and another variable factor to be integrated into system operation.
Compressed air has also been used to solve the problem of tails created by airless spray nozzles. See, for example, U.S. Pat. Nos. 3,202,363; 3,521,824; 3,635,400; 3,843,052; and 4,386,739 and Japanese patent publication No. 57-90762. In plural component spraying systems, compressed air has been used to assist in the atomization of plural component materials as shown, for example, in U.S. Pat. Nos. 2,780,496; 2,864,653; 3,799,403; and 4,618,098 and British patent specification No. 735,983.
External mix plural component systems originally included a plurality of separated spray gun or spray nozzles that were directed to blend their patterns together and to mix thereby resins and their catalysts or hardening agents. See, for example, U.S. Pat. Nos. Des. 252,097; 3,893,621; 4,123,007; 4,618,098; and 4,713,257.
In prior plural component application systems where the flow of plural component material is divided into many small streams, such as the system shown, for example, in European Patent No. 0,038,481, each of the streams tends to divide unpredicably and unreliably into segments of varying lengths, due to varying environmental factors and fluid flow characteristics, and the many streams of plural component material frequently create undesirable VOC emissions, that is emissions of volatile organic solvent vapors, such as styrene vapors, into the workplace.